sedimentary

Chert (Iron-stained)

Microcrystalline or Cryptocrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on the Mohs scale. Color: Tan, yellow-orange, or rusty brown due to iron oxide staining. Luster: Dull to waxy. Crystal structure: Trigonal (microscopic). Cleavage: None (conchoidal fracture). Specific gravity: 2.6-2.7.

Hardness: 7 on the Mohs scale
Luster: Dull to waxy

Identified March 29, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or through the chemical precipitation of silica in marine or groundwater environments. It typically forms as nodules or bedded layers within limestone or chalk. Age varies from Precambrian to Cenozoic.

Uses & applications

Historically used for prehistoric stone tools (knapping) due to its sharp edges. Modernly used in construction aggregate, road surfacing, surfacing of abrasive tools, and occasionally as an ornamental stone in jewelry (as Jasper).

Geological facts

Chert is so hard it can strike sparks from steel, a property that led to its use in 'flintlock' firearms. When it is red or highly colored, it is often called Jasper; when it is translucent and gray/black, it is called Flint.

Field identification & locations

Identify in the field by its extreme hardness (cannot be scratched by a steel knife) and its smooth, shell-like (conchoidal) breakage pattern. Often found in riverbeds or weathered out of carbonate rock outcrops.